0428同步年報-2021-全

3 D topological insulators (TI), which refer to the states of matter with an insulating gap in the bulk and gapless helical states on the surface, have attracted much attention due to their fascinating electronic structures. Proximity effects that occur in heterojunctions comprised of TIs and materials can provide an interesting platform to produce emerging quantum phenomena of Dirac fermions at the interfaces. For instance, it has been predicted that a hybrid structure made of a 3D TI and a superconductor can produce a superconducting proximity effect at the interface, which might lead to the emergence of 2D topological superconductivity hosting Majorana fermions. In graphene transferred on 3D TI, a strong proximity effect can induce opening of the band gap and strong spin- orbital coupling, which leads to a strong tunability and suppression of the spin signal and lifetime. Moreover, the predictions of such an interaction with non-topological states at the interface between a normal insulator (NT) and a TI might result in vertical twinning of the Dirac cone; the non-topological states can acquire a spin texture without magnetic doping. The study of the band structure of 2D NI/3D TI is significant to understand topological proximity effect; the results bear great potential for spintronics. Herein, Jung-Chun Andrew Huang (National Cheng Kung University), Tay-Rong Chang (National Cheng Kung University), Cheng-Maw Cheng (NSRRC) and their teams studied a novel phenomenon termed a topological proximity effect, which occurs between a 2D material and a 3D TI. To understand further the change of electronic structure between Sb 2 Te 3 and the antimonene/Sb 2 Te 3 hybrid heterostructure, they performed an experiment at TLS 21B1 beamline of the Taiwan Light Source recording angle-resolved photoemission spectra (ARPES) to probe the band structures. Figures 1(a) and 1(b) (see next page) show the band-mapping results of pristine Sb 2 Te 3 and antimonene/Sb 2 Te 3 recorded along the Г-K direction. In a comparison of the two band-mapping results along direction Г-K between Sb 2 Te 3 and antimonene/Sb 2 Te 3 , an additional Sb-bilayer (BL)-derived band is observed near the Fermi level; the band structure of Sb 2 Te 3 has a rigid band shift to larger binding energy. Figure 1(c) shows an enlargement of the energy scale in Fig. 1(b) to resolve the band dispersion around the Fermi level. The two Sb-BL- derived bands have an intersection at the Γ point near the Fermi level; a new Dirac point D sb is located almost at the Fermi level. The observed band dispersion indicates that a new topological state has been formed in the antimonene/ Sb 2 Te 3 hybrid-heterostructure. Figure 1(d) shows the calculated surface spectral weight with a color corresponding to the integrated charge Physics and Materials Science 013 A Route to Create Quantum Spin Hall Systems A novel phenomenon termed the topological proximity effect, which occurs between a 2D material and a 3D topological insulator, has generated a paradigm that opens a route to create quantum spin Hall systems in monolayer- substrate heterostructures. stabilize the CDW-Mott phase in terms of band engineering. The discovery of the robust CDW-Mott phase far above room temperature is considered valuable for developing practical CDW-Mott insulator-based ultrathin nanoelectronic devices. (Reported by Ashish Chainani) This report features the work of Takafumi Sato, Katsuaki Sugawara and their collaborators published in Nat. Commun. 12 , 5873 (2021). TLS 21B1 Angle-resolved UPS • ARPES • Materials Science, Condensed-matter Physics References 1. P. Fazekas, E. Tosatti, Philos. Mag. B 39 , 229 (1979). 2. K. Rossnagel, N. V. Smith, Phys. Rev. B 73 , 073106 (2006). 3. K. S. Novoselov, D. Jiang, F. Schedin, T. J. Booth, V. V. Khotkevich, S. V. Morozov, A. K. Geim. PNAS 102 , 10451 (2005). 4. Y. Nakata, K. Sugawara, A. Chainani, H. Oka, C. Bao, S. Zhou, P.-Y. Chuang, C.-M. Cheng, T. Kawakami, Y. Saruta, T. Fukumura, S. Zhou, T. Takahashi, T. Sato, Nat. Commun. 12 , 5873 (2021).